EP0228765A2 - Dispositif pour déterminer la position de la surface d'un objet, en particulier l'épaisseur d'une couche - Google Patents

Dispositif pour déterminer la position de la surface d'un objet, en particulier l'épaisseur d'une couche Download PDF

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Publication number
EP0228765A2
EP0228765A2 EP86307503A EP86307503A EP0228765A2 EP 0228765 A2 EP0228765 A2 EP 0228765A2 EP 86307503 A EP86307503 A EP 86307503A EP 86307503 A EP86307503 A EP 86307503A EP 0228765 A2 EP0228765 A2 EP 0228765A2
Authority
EP
European Patent Office
Prior art keywords
radiation
image
normal
workpiece
scattered
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86307503A
Other languages
German (de)
English (en)
Other versions
EP0228765A3 (fr
Inventor
Geoffrey Russell Court
Anthony Redvers Daborn
Michael Anthony Houlden
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ar Engineering Ltd
University of Liverpool
Original Assignee
Ar Engineering Ltd
University of Liverpool
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ar Engineering Ltd, University of Liverpool filed Critical Ar Engineering Ltd
Publication of EP0228765A2 publication Critical patent/EP0228765A2/fr
Publication of EP0228765A3 publication Critical patent/EP0228765A3/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating

Definitions

  • a powdered coating material such as a metal or a metal oxide
  • a powdered coating material is fed into the flame of an oxyacetylene torch which is directed at a workpiece to be coated.
  • the coating material is melted as it meets the flame, and is propelled with the flame at high speed towards the workpiece.
  • the high speed of the molten particles causes them to adhere firmly to the workpiece.
  • the amount of material applied during each pass can vary considerably, especially because of changes in the moisture content of the powdered coating material. This causes difficulties when a plurality of coated components is being produced to a single tolerance, because the critical dimensions of a workpiece can only be checked when the workpiece has been stopped from rotating and after it has cooled down to a temperature close to ambient temperature. Then a measurement can be taken with a micrometer.
  • the use of an oxyacetylene torch causes the temperature of the workpiece to rise considerably, and it takes a considerable time for the workpiece to cool sufficiently to allow measurements to be made.
  • the surface of the coating may be contaminated, e.g.
  • a device for monitoring the displacement of a point or portion on the surface of an object in a direction substantially parallel to the normal to the surface which device comprises a source of electromagnetic radiation which projects radiation onto the surface of the object in a direction inclined to the said normal, means for forming and detecting an image of radiation scattered from the surface in a direction inclined to the direction of the incident radiation and means for detecting the displacement of the position of the image in a direction substantially perpendicular to the direction in which the scattered radiation is detected arising from displacement of the surface in the direction of the normal.
  • the direction in which radiation scattered from the surface is detected may be substantially parallel to the normal to the surface.
  • the object may be rotating, and there may be means for indicating when a signal produced at the detection means is to be measured, so that signals are produced at a given angular orientation of the object.
  • the means for monitoring the displacement of a particular point or portion preferably comprise triggering means which sends a signal to a control device when the object is in a given orientation which, after a certain delay, measures the displacement of the image.
  • the device may be used to monitor the thickness of a coating being applied to the object, e.g. the thickness of metal or paint.
  • the direction in which radiation scattered from the surface is detected may be substantially parallel to the normal to the surface.
  • a monitoring device 18 is positioned approximately lcm from the surface of the workpiece. This is shown, diagrammatically, in more detail in Fig.2, and it comprises a first focussing lens 20, of 3 cm focal length, and with its optical axis normal to the workpiece surface, a mirror 21 inclined at an angle of 22.5 degress to the normal, a second focussing lens 22, of 1.8 cm focal length, and with its optical axis normal to the workpiece surface, and a 256 channel linear array charge coupled optical detector 24.
  • the optical detector is a one- dimensional array approximately 13 microns by 0.3 cm of 256 high sensitivity photocells, the outputs of which may be analysed by a microprocessor 25.
  • a quartz iodine projector lamp 26 (Fig.l) is fed along an optical fibre 28 of 100 microns diameter to the first focussing lens 20, and the light is focussed on the uncoated surface of the workpiece 10 at an angle of 45 degrees to the normal.
  • the monitoring device is mounted in a strong metal casing 34 which is airtight except for a surface viewing aperture 36 in the face of the casing adjacent the workpiece, through which aperture light is projected and scattered back to the detector 24.
  • a flexible tube 38 supplies clean compressed air to the interior of the device, through an aperture in the rear of the casing. The air supply keeps the . components of the device cool, and the flow of air out of the viewing aperture prevents coating powder from entering the casing and thus contaminating the components.
  • a triggering device 30 is provided, and comprises an optical detector and a light emitting diode mounted adjacent to each other, which are positioned about 1 cm from the rotating chuck 14. Light from the light emitting diode is projected onto the rear face of the chuck 14, and positioned on the rear face of the chuck, in the path.of the light which is projected thereon, is a small polished metal reflector (not visible in Fig.l). When the reflector is opposite the device 30, light from the light emitting diode is reflected back to the optical detector in the triggering device and a signal is sent to the controlling microprocessor 25.
  • the detection of a triggering signal by the triggering device allows measurement to take place at a specific location on the workpiece, irrespective of the rotational accuracy of the workpiece, and so accurate centring of the workpiece on the lathe is not critical.
  • the workpiece 10 is mounted in the lathe and the lathe is switched on.
  • the workpiece rotates, light from the optical fibre 28 is focussed and reflected onto the surface of the workpiece, shown as point X in Fig.2.
  • Light scattered from the surface of the workpiece is focussed by lens 22 onto the charge coupled optical detector 24.
  • the triggering device is used to synchronise the measurement.
  • the microprocessor measures and records the signals from the detector 24. An operator will have instructed the microprocessor previously for how long the signal from the detector is to be measured.
  • the application of the metal coating then begins.
  • the device 16 applies a metal coating to the workpiece, between the limits desired, by moving parallel to the axis of rotation of the lathe.
  • this coating forms a layer 42, shown highly exaggerated as a dotted line in Fig.2, of thickness z on the surface of the workpiece, and as can be seen from Fig.2 the scattering of the incoming light occurs at a point X' which is at a distance x along the surface of the workpiece towards the incoming light.
  • Light is scattered from X' and is focussed by lens 22 into an image I' on the detector 24. This is shown in dotted lines in Fig.2.
  • application of a coating of thickness z causes the image of the light scattered from the surface to be displaced through a distance Z on the detector 24.
  • the device can be calibrated to find M, from which the thickness of the layer can be determined by detection of the displacement y at the detector 24. Calibration is performed by taking a zero measurement of y with an uncoated workpiece, then moving the monitoring device by a predetermined amount and taking a measurement of displacement of the image. Since the magnification M can be determined, and its value stored in the microprocessor so that values of z may be displayed directly.
  • the image I' of the spot of light will not be in focus because the incoming light is focussed on the actual surface of the workpiece while the scattering takes place from the surface of the coating. However, the image I' will be spread over a plurality of the photocells of the detector 24, and by analysing the signal from each of the photocells the microprocessor can determine the spot profile and calculate the centre of the image I' and hence the displacement y.
  • the theoretical optimum position resolution with the system is 7 um, but the best value obtained is 25 um.
  • the above parameters give a reading range of 0.1 cm.
  • the device as described can measure the change in radius of a rotating object which is being spray coated to an accuracy better than 1 thou (25 microns).
  • the embodiment described above uses the ability of the CCD 24 to store (integrate) the reflected electromagnetic radiation over a period of time.
  • the CCD is not being used as a binary on/off switch, but rather the data is being captured in a form which lets the mean value, or centre, of the distribution be found using mathematical or statistical methods. It is this which gives this embodiment its precision, because the roughness of the surface is 'averaged out' by scanning over a small section of the moving surface. Were this averaging not done, i.e.
  • the data from the CCD would not be a smooth peak, but one with sharp peaks, which would shift their position dramatically as different parts of the surface are scanned. In that event, it would not be possible to define what is meant by the centre of the peak, and the precision of the method would be lost.
  • the temperature of the workpiece will increase during coating and the workpiece will expand, thus producing incorrect readings for when the workpiece is cool.
  • calibration can be carried out on a heated uncoated workpiece, or alternatively a temperature profile, comprising the expansion of the workpiece on successive passes of the spray gun, may be store in the microprocessor which the compensates automatically.
  • a micro-switch operated by the spray gun may give information to the microprocessor as to how many passes have been made.
  • the time interval over which the data can be captured is decided by electronic means, e.g. by triggering at a particular part of the rotation cycle, a scan around the circumference of a rotating object can be made by introducing a variable delay between the trigger signal and the time of data capture. This means that the sensing head can be kept stationary while the work rotates under it, rather than having to move the sensing head around the work.
  • the microprocessor may be arranged to measure the position of the image I and the corresponding displacement y of the image I' at a plurality of different times after the triggering signal has been received, or, if the run-out of the workpiece is found to be small, the position of the image I' may be detected over a larger portion of a revolution of the workpiece. In the latter case, the signal would be averaged out, and an average value of the coating thickness would be obtained.
  • a quartz iodine projector lamp instead of a quartz iodine projector lamp, other light sources may be used. If the run-out of the workpiece is large and/or if the workpiece is rotating rapidly, measurement of the scattered light must be taken over a short period of time. Thus, the intensity of the light source must be increased in order for sufficient light to be scattered to the detector.
  • a laser may be used in this case. For very high speeds of revolution, i.e. very short periods of measurement, a pulsed laser may be used, and the pulses of the laser may be used instead of the triggering device 30 to produce a triggering signal.
  • a light emitting diode may be mounted in the monitoring device. Again, for very high speeds of revolution, the light emitting diode may be pulsed, whose pulses may too be used for triggering purposes.
  • the invention is not restricted to measuring the thickness of an applied coating. It may be used where it is desired to monitor continuously the position or displacement of an object. For example, it may be used to measure the expansion of a turbine blade in a turbine. All such measurements are remote and do not affect the operation of the object in question.
  • the monitoring device becomes more sensitive, and the output of the detecting device may be used to gain information on the surface profile of the workpiece.
  • the workpiece need not be rotating, and a surface of a stationary object may have its profile analysed.
  • the signals detected by the plurality of photocells may be used to reveal directly the microscopic surface profile of the object.
  • the basic technique can also be used to measure the machining off of material in a lathe, with the advantage that because it measures from the surface of the work, the effect of tool wear is eliminated.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
  • Length Measuring Devices By Optical Means (AREA)
EP86307503A 1985-10-01 1986-10-01 Dispositif pour déterminer la position de la surface d'un objet, en particulier l'épaisseur d'une couche Withdrawn EP0228765A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8524145 1985-10-01
GB858524145A GB8524145D0 (en) 1985-10-01 1985-10-01 Monitoring device

Publications (2)

Publication Number Publication Date
EP0228765A2 true EP0228765A2 (fr) 1987-07-15
EP0228765A3 EP0228765A3 (fr) 1989-02-22

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP86307503A Withdrawn EP0228765A3 (fr) 1985-10-01 1986-10-01 Dispositif pour déterminer la position de la surface d'un objet, en particulier l'épaisseur d'une couche

Country Status (2)

Country Link
EP (1) EP0228765A3 (fr)
GB (1) GB8524145D0 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4425187A1 (de) * 1994-07-16 1996-01-18 Mtu Muenchen Gmbh Verfahren und Vorrichtung zum Messen von Schichtdicken
EP1643209A3 (fr) * 2004-09-30 2012-07-25 Alstom Technology Ltd Procédé de mesure de l'épaisseur d'une couche
CN108549759A (zh) * 2018-03-30 2018-09-18 苏州瀚华智造智能技术有限公司 一种针对自动化喷涂工艺的零件涂层厚度计算和仿真方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1427430A (fr) * 1964-03-14 1966-02-04 Exatest Messtechnik Gmbh Dispositif de mesure pour déterminer au moyen d'un rayonnement l'épaisseur d'un matériau sans le toucher
US3645623A (en) * 1970-09-25 1972-02-29 Raymond A Patten Apparatus for monitoring film thickness by reflecting a light beam from the film surface
DE2701858A1 (de) * 1976-01-19 1977-07-21 Nat Res Dev Messverfahren und -vorrichtung fuer abstandsaenderungen
GB1484996A (en) * 1974-09-06 1977-09-08 United Biscuits Ltd Measurement of the position of a surface
JPS56120904A (en) * 1980-02-29 1981-09-22 Chugoku Toryo Kk Measuring method for rate of removal of coating film
EP0121617A1 (fr) * 1983-04-07 1984-10-17 Armco Inc. Méthode et appareil pour mesurer l'usure d'un garnissage réfractaire

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1427430A (fr) * 1964-03-14 1966-02-04 Exatest Messtechnik Gmbh Dispositif de mesure pour déterminer au moyen d'un rayonnement l'épaisseur d'un matériau sans le toucher
US3645623A (en) * 1970-09-25 1972-02-29 Raymond A Patten Apparatus for monitoring film thickness by reflecting a light beam from the film surface
GB1484996A (en) * 1974-09-06 1977-09-08 United Biscuits Ltd Measurement of the position of a surface
DE2701858A1 (de) * 1976-01-19 1977-07-21 Nat Res Dev Messverfahren und -vorrichtung fuer abstandsaenderungen
JPS56120904A (en) * 1980-02-29 1981-09-22 Chugoku Toryo Kk Measuring method for rate of removal of coating film
EP0121617A1 (fr) * 1983-04-07 1984-10-17 Armco Inc. Méthode et appareil pour mesurer l'usure d'un garnissage réfractaire

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
MEASUREMENT AND CONTROL, vol. 16, no. 12, December 1983, pages 468-470, Dorking, GB; M. FABIAN: "Optical measurement techniques using laser diodes (Part 2)" *
PATENT ABSTRACTS OF JAPAN, vol. 5, no. 201 (P-94)[873], 19th December 1981; & JP-A-56 120 904 (CHIYUUGOKU TORIYOU K.K.) 22-09-1981 *
PROCEEDINGS OF THE 5TH ANNUAL ISA TEST MEASUREMENT SYMPOSIUM, New York, 28th-31st October 1968, vol. 5, pages 1-5; R.B. ZIPIN: "Non-contact optical fiducial" *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4425187A1 (de) * 1994-07-16 1996-01-18 Mtu Muenchen Gmbh Verfahren und Vorrichtung zum Messen von Schichtdicken
EP1643209A3 (fr) * 2004-09-30 2012-07-25 Alstom Technology Ltd Procédé de mesure de l'épaisseur d'une couche
CN108549759A (zh) * 2018-03-30 2018-09-18 苏州瀚华智造智能技术有限公司 一种针对自动化喷涂工艺的零件涂层厚度计算和仿真方法

Also Published As

Publication number Publication date
GB8524145D0 (en) 1985-11-06
EP0228765A3 (fr) 1989-02-22

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